My first duster had somewhat of a similar mismatch combination and definitely what people are saying about the torque converter that's just too much to hold at a light with that Cam. And it doesn't idle well. I do remember one specific thing that you may try. I remember anytime I put anything less than super unleaded in it it would run like total crap and not idle and actually run as if it was on six or four cylinders. The driving around a little bit and get good gas in it and finally it would start running good.
